STUDIA CHEMIA - Issue no.1 / 2025 - Table of contents

This paper presents the results of our research concerning the feasibility of the Fe, Ni and Zn electroextraction from partially treated spent leaching solutions resulting from the waste printed circuit boards recycling process using the bromine/bromide system. The first tests, performed in a real sample of spent leaching solution and using a Pt Fisher type cathode, led to inacceptable results due to the intensive hydrogen evolution. To find a feasible industrial solution, systematic preliminary tests were performed by hydrodynamic cyclic voltammetry in synthetic solutions using small diameter (3 mm) rotating disk electrodes (RDEs) of carbon paste (CP) and 304 type stainless steel (304 SS), resulting in theoretical current efficiencies of up to 95.8%. Further, to prove the feasibility of the pure Zn and Zn alloys electroextraction, long duration (0.15÷8 h) experiments were done by potentiostatic chronoamwperometry using RDEs on CP and 304 SS of large diameters (38 and 29 mm, respectively). The obtained results proved that, depending on the electrolyte’s composition and pH, and on the imposed potential, high purity Zn (over 98%) or Zn-Fe-Ni alloy deposits can be obtained at current efficiencies between 20 and 96% and specific energy consumptions between 2 and 17 kWh/kg of alloy.

Keywords: waste printed circuit boards recycling, selective electroextraction, iron, nickel and zinc recovery, iron-nickel-zinc alloy electrodeposition

Tetra Pak® (TP) multilayer packaging consisting of paper, polyethylene (PE) and aluminum, are widely used as aseptic packages in the food and beverage industry. Consequently, large quantity of packaging waste is generated, and many efforts have been made for recycling. The aim of this work was to develop new composite materials from TP cartons waste by thermoplastic method at different temperatures ranging from 120 ºC to 140 ºC. The resulting material was characterized by thermogravimetric/differential thermal analyses (TG/DTA) and differential scanning calorimetry (DSC) measurements to establish the thermal behavior of the prepared composites. Based on these results, the degradation pathway of the composites obtained from TP waste was proposed. The results of the study show that the preparation of thermoplastic composites represents a promising recycling process. The thermal degradation temperature of the prepared composites establishes a limit for practical use, which prohibits the utilization of these materials at temperatures exceeding this threshold.

Keywords: Tetra Pak® waste, recycling, composite materials, thermal degradation

Activated carbon from quinoa straw, an agricultural waste, was prepared by chemical activation using a novel activator, rubidium chloride. The effects of time, temperature and amount of activator on the yield and adsorption properties of quinoa straw activated carbon were also investigated. The results showed that the optimal activation process for quinoa straw activated carbon was: activation temperature 700 ℃, activation time 2 h, and RbCl-QS ratio 1:1. The quinoa straw activated carbon prepared under this process had a yield of 27.18%, an iodine adsorption value of 828.11 mg g-1, a total pore volume of 0.303 cm3 g-1, a major pore size of 0.58 nm, and a specific surface area of 635.59 m2 g-1. At room temperature and pressure, the H2 desorption can reach 3.92 cm3 g-1. quinoa straw activated carbon prepared using RbCl as activator has excellent adsorption and hydrogen storage properties.

Keywords: Ultra-microporous, Activated carbon, Hydrogen adsorption storage, Chenopodium quinoa Willd., rubidium chloride

The focus of this work is on the functionalization of gold nanoparticles, GNPs, with doxorubicin, D, an anticancer drug, both in the absence and in the presence of natural adjuvant biomolecules, like piperine, P, resveratrol, R, resveratrol-piperine, RP, complex, and icariin, I, which are therapeutic molecules with demonstrated anticancer and anti-inflammatory activity, to form highly stabilized colloidal dispersions. The green syntheses of GNPs, as cores, loading self-assemblies of various selected biomolecules, adsorbed on their surface, as shells, was confirmed by observing surface plasmon resonance at about 538 nm. Further, gold nanoparticles stabilized by resveratrol, GNP-R, are functionalized with various concentrations of selected biomolecules: D, P, R, RP, and I, resulting in different D/P/R/RP/I@GNPs-R composite nanoparticles for various compositions. Another series of stabilized colloidal dispersions is generated as GNP-R1, where the initial GNP-R is centrifuged and washed and then it is dispersed in aqueous solutions and further functionalized with said selected biomolecules. This study proves the functionalization of GNPs, as composite nanoparticles of high stability, in the presence of phosphate buffer saline, PBS, as confirmed by UV-Vis spectra of their colloidal aqueous dispersions.

Keywords: gold nanoparticles, doxorubicin, adjuvant anticancer molecules, UV-Vis spectroscopy, surface plasmon resonance

Natural compounds, such as trans-resveratrol, R, piperine, P, and icariin, Ic, have antioxidant and anti-inflammatory properties, and potential anticancer activity. Gold nanoparticles, GNPs, are biocompatible and can be used as carriers for biomolecule delivery, improving their performance at a small dose. The aim of the present study was to synthesize GNPs with sodium citrate, noted GNP_C (or GNP-C), and enhancing their stability and anticancer activity by functionalization with R, P, Ic, asparagine, A, and doxorubicin, D, as a standard drug. The obtained GNPs as cores, loading selected biomolecules, adsorbed on their surface as shells, were characterized by various methods, UV-Vis spectroscopy, XRD, AFM, TEM, and particle size analysis. The anticancer activity of functionalized GNP_C was evaluated using MTT assay in four human cell lines: breast cancer, MDA-MB-231 and MCF-7 cell lines, tumor stem cells (isolated from glioblastoma), a GM1 cell line, and a normal (healthy) stem cell line derived from a dental follicle, DF. GNP_C functionalized with R, P or Ic exhibited an anticancer activity comparable to GNP_C functionalized with doxorubicin for low concentrations in gold and in natural compounds, thus reducing side effects of anticancer drug. These promising results need further examination using various cell lines and animal models, to clinical applications

Keywords: functionalized gold nanoparticles, cytotoxicity and anticancer activity, cancer cell lines

The development of cost-efficient and sustainable methods for the synthesis of nanomaterials still remains a scientific challenge. The aim of this study was to investigate the green synthesis of silver nanoparticles using aqueous extract of Galium verum L. (GV) as a potential source of biomolecules able to reduce the silver ions and stabilize them. Reaction parameters such as concentrations of AgNO3, extract to AgNO3 ratio, temperature, pH, and reaction time were optimized. The synthesis of silver nanoparticles (GV-AgNPs) using different parameters was monitored by ultraviolet-visible spectroscopy (UV-Vis). Fourier transform infrared spectroscopy (FTIR) results showed the presence of functional groups that act as reducing agents and stabilize the GV-AgNPs. Atomic force microscopy (AFM) confirmed that the particles were round-shaped with a diameter of about 25 nm. The GV-AgNPs show different antimicrobial activity depending on the type of sample and depending on the microbial strain tested.

Keywords: green synthesis, nanoparticles, galium verum, antimicrobial activity

The title compound was prepared from MnCl2 · 4 H2O in the presence of KSCN and 4,4’-diaminobiphenyl (DABPh), using ethanol as a solvent. The complex was thoroughly characterized by elemental analysis, IR spectroscopy, and single crystal X-ray diffraction. The coordination mode of the SCN⁻ anion (i.e. Mn – NCS vs. Mn – SCN) was investigated, and it was found that in the solid state the manganese(II) ion is coordinated by two SCN⁻ ligands N-bonded to the metallic center. The coordination sphere around the metal also contains two DABPh and two ethanol molecules. The supramolecular structure of the complex is held together by several O – H ··· N and N – H ··· S hydrogen bonds. These interactions build up a 3D grid with the Mn atoms positioned in the corners of an 8.548 Å x 13.809 Å x 14.622 Å parallelepiped.

Keywords: Manganese(II), 4,4’-diaminobiphenyl, isothiocyanate, single crystal X-ray diffraction structure, hydrogen bonds, supramolecular structure.

This study investigates the binding of ferrocenylmethyl nucleobase derivatives to DNA through electrostatic interactions, employing a combination of experimental and theoretical approaches to elucidate binding mechanisms and explore their potential for DNA targeting. UV–Vis spectroscopy and cyclic voltammetry (CV) were used to evaluate binding affinities and structural alterations in DNA. The derivatives exhibited DNA interactions, evidenced by negative formal potential shifts in CV data. Binding constants and free binding energies derived from docking simulations aligned well with UV–Vis and CV analyses. Additionally, voltammetric data provided insights into the binding site size. Molecular docking simulations confirmed the critical role of electrostatic interactions in the binding of FcMeCy, FcMeTh, and (FcMe)2Ad to DNA. Molecular dynamics simulations further revealed the stability of DNA-ligand complexes, with RMSD and radius of gyration (Rg) analyses indicating compact and stable DNA structures, emphasizing the robustness of these interactions for therapeutic applications. Theoretical investigations, including geometry optimization, Mulliken charge distribution, molecular electrostatic potential (MEP) analysis, and HOMO-LUMO surface analysis using density functional theory (B3LYP/aug-cc-pVTZ/6-311++G(d,p)), offered deeper insights into structural properties, reactive sites, and chemical reactivity. These results provide a comprehensive understanding of the interaction mechanisms and potential applications of these derivatives.

Keywords: Ferrocene Nucleobase, Molecular dynamic simulation, Molecular docking, DFT

Agriculture plays a role in greenhouse gas (GHG) emissions, especially by cultivating biofuel crops like rapeseed (Brassica napus). This study assesses the GHG emissions associated with rapeseed farming in Romania, focusing on 2022–2024. Data were collected from rapeseed cultivation at Mihai Viteazu, Cluj, under various fertilization and irrigation conditions. The study reveals that GHG emissions range from 89 to 231 kg CO2 eq/l biodiesel, with irrigation reducing emissions by approximately 1.3 times compared to non-irrigated conditions. Notably, nitrogen fertilization significantly increases nitrous oxide (NOx) emissions, which account for 80% of total GHG emissions, particularly under higher nitrogen application rates. The results highlight the need for optimized nitrogen management to balance yield increases with environmental impacts, as excessive nitrogen use intensifies NOx emissions due to enhanced nitrification and denitrification processes. The study also finds that irrigation mitigates GHG and NOx emissions, emphasizing its role in sustainable rapeseed farming. This research underscores the importance of precision nitrogen management and irrigation in reducing the carbon footprint of rapeseed biodiesel production while enhancing crop productivity in Romania.

Keywords: greenhouse gas emissions, GHG, rapeseed farming, nitrogen fertilization, biofuels, sustainable agriculture

Unwanted scale deposits cause numerous technical and economic problems and, for this reason, it is desired to inhibit their formation. The paper studied the possibility of using guar gum and xanthan gum as scale inhibitors mainly in the food industry, due to the fact that they are biodegradable and non-toxic. The two gums, with concentrations between 50 and 100 mg/L, have proven their effectiveness in the case of waters with initial total hardness below 10 mval/L. The scaling inhibition capacity was also correlated with the variation in electrical conductivity of the water samples. X-ray diffraction analysis of CaCO3 scale formed in waters with initial total hardness over 10 mval/L, stationed for 24 hours in a thermostatic oven at 80°C, demonstrates the presence, mainly, of two polymorphic forms, calcite and aragonite.

Keywords: calcium carbonate, guar gum, hardness, inhibitor, water scales, xanthan gum

The purpose of this work is to concurrently estimate the UV-visible spectra of binary combinations of piroxicam and mefenamic acid using the chemometric approach. To create the model, spectral data from 73 samples (with wavelengths between 200 and 400 nm) were employed. A two-layer artificial neural network model was created, with two neurons in the output layer and fourteen neurons in the hidden layer. The model was trained to simulate the concentrations and spectra of piroxicam and mefenamic acid. For piroxicam and mefenamic acid, respectively, the Levenberg-Marquardt algorithm with feed-forward back-propagation learning produced root mean square errors of prediction of 0.1679 μg/mL and 0.1154 μg/mL, with coefficients of determination of 0.99730 and 0.99942, respectively. The suggested approach’s ease of use, affordability, and environmental friendliness make it a suitable replacement for the use of hazardous chemicals in the routine investigation of the selected drugs.

Keywords: piroxicam, mefenamic acid, concurrent estimation, artificial neural networks model

Cannabidiol (CBD) oils and products have become extremely popular in the last decade. These products are marketed as having different effects and are recommended for many chronic diseases. Various food supplements with CBD are now available on the market, but due to legislative lacks the declared concentration of CBD and other cannabinoids in the products is often significantly different compared with the real concentration. Products that don't meet quality criteria result from a lack of control and standardization. The aim of this study was to develop and validate an LC-MS/MS method for the routine quantification of cannabinoids in herbal drugs and food supplements. An LC-MS/MS method was developed using an UHPLC system coupled with a QTOF mass spectrometer, and the chromatographic separations were performed on a C18 column with isocratic elution, electrospray ionization in negative mode with a run-time of 10 minutes. According to the international guidelines, the method was validated concerning linearity, selectivity, stability, precision, and accuracy. Out of the ten tested products, in three of the supplements, significant differences were noticed in CBD concentration compared to the declared content. Other cannabinoids were also identified in some of the samples. This study raises awareness regarding insufficient controlled food supplements.

Keywords: cannabinoids, cannabidiol, LC-MS/MS, food supplements

A simple, cheap, and sensitive analytical method was validated for the determination of copper in human hair after microwave digestion. Method validation parameters such as linearity, precision, accuracy, limit of detection (LOD) and limit of quantification (LOQ) were determined. A graphite furnace atomic absorption spectrophotometer has been used. The developed method was linear in the concentration range of 2 - 20 μg/L with a 0.9979 coefficient of determination. The recoveries obtained for the copper ranged from 90.46-94.96%, with a precision not exceeding 3.95% relative standard deviation (RDS%) and system suitability test with RSD% lower than 1.58%. LOD was found to be 0.05632 μg/g and LOQ 0.18745 μg/g. The analyzed samples were from healthy humans and the study shown similar concentration of copper in hairs collected from adult, teenager men and female. The proposed method was considered adequate for the determination of copper in hair samples.

Keywords: GFAAS, hair, copper, validation

New chemometric smart approaches, Artificial Neural Network (ANN) and Continuous Wavelet Transform (CWT), based on UV spectrophotometric data, were proposed for the simultaneous quantitative analysis of ciprofloxacin and ornidazole in tablets. Both methods enabled the study of the two-component mixtures containing these drugs without requiring a pre-separation process. The ANN calibration model was developed by establishing a relationship between the absorbance measurement matrix and the calibration set, which was constructed using a full factorial design methodology. To quantify ciprofloxacin and ornidazole, Symlets8 continuous wavelet transform (sym8-CWT) exhibited to be a suitable tool for transforming the UV spectra during the calibration and prediction stages. Both chemometric methods were applied within the linear working range of 3–24 μg/mL for ciprofloxacin (CIP) and 6–32 μg/mL for ornidazole (ORN). The validity of the proposed ANN and sym8-CWT approaches was confirmed through the analysis of independent test samples, as well as intra-day, inter-day, and standard addition experiments. The ANN method provided impressive recovery rates of 99.9% for CIP and 100.1% for ORN. Similarly, the sym8-CWT method achieved recovery rates of 98.5% for CIP and 101.5% for ORN. Both ANN and sym8-CWT approaches were successfully applied to the real sample analysis of CIP-ORN tablets, demonstrating precise and accurate results at a low cost and with minimal sample preparation.

Keywords: UV-Spectrophotometry, Artificial Neural Network, Continuous Wavelet Transform, Ciprofloxacin, Ornidazole

This study examines the rheological behavior of three Algerian crude oils, focusing on steady flow, yield stress, and thixotropic behavior across temperatures. The oils exhibit non-Newtonian pseudoplastic behavior with a yield stress at the onset of flow. Results show that viscosity and shear stress decrease with temperature, reducing yield stress and improving flow. The Herschel-Bulkley model best fits crude oil 1, while the Casson model is more suitable for oils 2 and 3 at 30°C, and the power law and Herschel-Bulkley models apply at 20°C. Over the 20–50°C range, apparent viscosity and shear stress decrease by 71%, 77%, and 79% for oils 1, 2, and 3, respectively, while yield stress drops by 24.4%, 48.5%, and 54%. Thixotropic behavior is also observed, with reduced hysteresis area at higher temperatures, indicating reduced internal friction. These findings highlight the role of temperature in enhancing crude oil flow properties, suggesting heat treatment improves transportability.

Keywords: Crude oil, rheology, temperature, thixotropy, viscosity, yield stress